Expression of the mdr1 gene may be an important cause of chemotherapy failure in patients with Non-Hodgkin's Lymphoma. ONCEP (Vincristine [O], Novantrone [N], Cyclophosphamide [C], Etoposide [E], and Prednisone [P]) chemotherapy contains three MDR (Multi-drug resistance)-related agents (O, N, E) and was designed for studies of MDR modulation. PSC 833 is a non-immunosuppressive cyclosporine with greater in vitro MDR modulating activity than Cyclosporin A. ONCEP-PSC chemotherapy is well tolerated and has significant activity in patients with recurrent or refractory NHL.